Rewiring TLROM cart for use with W27E512

Rewiring TLROM cart for use with W27E512
by tokumaru on 2006-04-17 (#12005)

Hi guys. I have successifully completed 2 NROM devcarts so far, but that was easy because they didn't need any rewiring for use with the Flash ROMs I have.

Yesterday, I tried something more difficult, and removed the ROMs of a TLROM cart. The largest chips I have around are W27E512, wich are 64KBytes and can be erased with the EPROM programmer. I figured it'd be OK, I'd be using half the capacity of the board, but that's OK.

This chip's pinouts go like this:

Code:

       ---_---
A15 - |01   28| - Vcc
A12 - |02   27| - A14
A7  - |03   26| - A13
A6  - |04   25| - A8
A5  - |05   24| - A9
A4  - |06   23| - A11
A3  - |07   22| - OE/Vpp
A2  - |08   21| - A10
A1  - |09   20| - CE
A0  - |10   19| - Q7
Q0  - |11   18| - Q6
Q1  - |12   17| - Q5
Q2  - |13   16| - Q4
GND - |14   15| - Q3
       -------

I was happy, because it almost matches the NES ROM, except pin 22 is not A16, it's OE. Since I usually see OE beeing connected to GND, I did that, and left hole 22 empty.

As for the CHR part, It puzzles me why Nintendo used different chips if they are the same size. Does anyone know why? Anyway, if I placed my chip on the bottom 28 pins, CE and OE would be on the wrong place, and would have to be soldered to holes 31 and 02, respectivelly.

It all seemed fine to me, except it didn't work. All I got was a grey screen. I wasn't upset or anything, 'cause I kinda expected that to happen. Do you see anything wrong with what I did? In the PRG chip, is OE supposed to be connected to GND? Does anything else need to be done?

Thanks for the help again.

Oh, and what does an "/" mean on these pinouts? I don't understand why there is a pin (31) in the CHR ROM labeled "/A13".

by tepples on 2006-04-17 (#12006)

The prefix / means inverted or active-low.

by tokumaru on 2006-04-17 (#12007)

I see... but what does "/A13" have to do with "CE" then? How does inverted or active-low A13 relates to CHIP ENABLE? I don't understand why they are on the same pin.

by Memblers on 2006-04-17 (#12008)

Since it's A13, then it'll be active when the PPU accesses $2000 and higher (name tables), and inactive when PPU accesses $1FFF and lower (pattern tables).

by tokumaru on 2006-04-18 (#12032)

Oh, come on guys... I'm really new at this and need some help. Many of you have been doing this kind of stuff for a while and this is probably piece of cake for you (Memblers, you design your own boards! That's huge!)...

But for me... I'm kinda guessing here, based on the documented rewiring, but I must have done something wrong, since I can't get it to work. Can't you point to me what I did wrong?

I don't know if you have to do something about the empty holes or you can just leave them like that... I don't know exactly what to do when no CE or OE pins/holes are present... And you know, it's kind of hard for me to get new carts to modify, and I'd like to go through this without making any of them useless...

Thanks for the help again.

by Memblers on 2006-04-18 (#12033)

Well I guess we could deal with PRG first, since you're getting a grey screen it must not be working. If you're putting a 28-pin ROM into a 32-pin socket, the rewiring guides probably don't cover that case. Best thing to do would be to view your chip's datasheet/pinout and compare it to the pinout of the ROM you're replacing.

At any rate, both /CE and /OE must be hooked up to something. Two possible ways, first is to connect /OE to GND and /CE to the PRG/CE pin on the board. Or connect /CE to GND and /OE to PRG/CE.

by tokumaru on 2006-04-18 (#12034)

Memblers wrote:
Well I guess we could deal with PRG first, since you're getting a grey screen it must not be working.

That's what I thought. When I first tried to run Mario with the wrong CHR (in the NROM board) I at least could see that the palettes were set and such.

Quote:
If you're putting a 28-pin ROM into a 32-pin socket, the rewiring guides probably don't cover that case.

Actually, at least in the board I used (Nintendo World Cup), the PRG chip was 28-pin, only the CHR chip was 32-pin. Pretty weird to me, as both were supposed to be 128 KBytes...

Quote:
Best thing to do would be to view your chip's datasheet/pinout and compare it to the pinout of the ROM you're replacing.

When I put them side to side:
Code:
W27E512: NES PRG ROM:

---_--- ---_---
A15 - |01 28| - Vcc PRG A15 - |01 28| - +5V
A12 - |02 27| - A14 PRG A12 - |02 27| - PRG A14
A7 - |03 26| - A13 PRG A7 - |03 26| - PRG A13
A6 - |04 25| - A8 PRG A6 - |04 25| - PRG A8
A5 - |05 24| - A9 PRG A5 - |05 24| - PRG A9
A4 - |06 23| - A11 PRG A4 - |06 23| - PRG A11
A3 - |07 22| - /OE/Vpp PRG A3 - |07 22| - PRG A16
A2 - |08 21| - A10 PRG A2 - |08 21| - PRG A10
A1 - |09 20| - /CE PRG A1 - |09 20| - PRG /CE
A0 - |10 19| - Q7 PRG A0 - |10 19| - PRG D7
Q0 - |11 18| - Q6 PRG D0 - |11 18| - PRG D6
Q1 - |12 17| - Q5 PRG D1 - |12 17| - PRG D5
Q2 - |13 16| - Q4 PRG D2 - |13 16| - PRG D4
GND - |14 15| - Q3 GND - |14 15| - PRG D3
------- -------

I see that only one pin is out of place, /OE, wich would be in the hole used for A16. Since my chip is 64 KBytes, I won't be using A16, so I connected pin 22 to GND and left hole 22 empty. That didn't work.

Quote:
At any rate, both /CE and /OE must be hooked up to something. Two possible ways, first is to connect /OE to GND and /CE to the PRG/CE pin on the board. Or connect /CE to GND and /OE to PRG/CE.

So inverting them is a possibility? Man, I'm feeling kinda stupid. Only one pin doesn't match, this should be a simple modification.

BTW, is the "/" we see in these ASCII pinouts the same as a line above the pin name, as seen in PDF datasheets?

by tepples on 2006-04-18 (#12035)

tokumaru wrote:
BTW, is the "/" we see in these ASCII pinouts the same as a line above the pin name, as seen in PDF datasheets?

Yes.

by Memblers on 2006-04-18 (#12038)

tokumaru wrote:
I see that only one pin is out of place, /OE, wich would be in the hole used for A16. Since my chip is 64 KBytes, I won't be using A16, so I connected pin 22 to GND and left hole 22 empty. That didn't work.

It sounds like that should've worked. What program do you have in the chip then? I would take a 16kB game and duplicate it until it fills the ROM up, so you'd know the mapper settings won't be able to crash a game.

And yeah, Nintendo's 128kB ROMs are 28-pin, I don't know why the CHR ones are 32-pin though.

by tokumaru on 2006-04-18 (#12039)

Memblers wrote:
It sounds like that should've worked.

I don't know if I'm glad or sad to hear that... O.o
I guess it is a good thing. I'll double check all connections with my multimeter and make sure everything else is OK.

Quote:
What program do you have in the chip then? I would take a 16kB game and duplicate it until it fills the ROM up, so you'd know the mapper settings won't be able to crash a game.

I did almost that, I wrote SMB1 twice. I didn't want to go through the trouble of slicing a MMC3 game down to 64k and have it still work. The repeated SMB ROM worked fine with emulators. Maybe I'd be safer with a 16k game, since, as you said, MMC3 wouldn't be able to mess that up, right?

Quote:
And yeah, Nintendo's 128kB ROMs are 28-pin, I don't know why the CHR ones are 32-pin though.

Very weird, IMO.

When I get home today I'll double check everything. Maybe I'll try this chip with the NROM cart, just to verify it works. And then when (if) I get PRG to work I'll try and figure out the problem with the CHR chip.

I just thought of something: is there a possibility that Vcc for this chip is not 5V? The datasheet I have for it is very cryptic, unlike the ones I found for my Flash ROMs, wich are very clear about the 5V. EDIT: I think I found it, it seems to be 5V, so that is not a problem.

by tokumaru on 2006-04-20 (#12093)

I'm taking a break from this, I'm really upset 'cause I ruined a perfectly good TLROM cart trying to remove the sockets I had soldered. I scratched the board, pulled a full trace out of it, it was a total mess.

I don't feel like ruining another board anytime soon, so I'm open to ideas on ways to try rewiring until I find the correct/working position of every pin and can solder the whole thing for good.

How do you manege to desolder a socket anyway? With the chips I found it easy since you can heat the pins from the chip side of the board and use a solder sucker on the other side. But with the sockets there is little or no visible part of the pins to heat up on the chip side. Sucking from the same side as the soldering iron never gets all the solder out.

I tried to get an iron with a sucker attached, but I didn't find anything like this here. I found some really expensive (around $400) soldering stations, but those are way out of my price range and are probably much more than what I need.

by Lloyd Gordon on 2006-04-24 (#12189)

Don't get upset. The boards are really hard to completely destroy. I've ripped out traces, cracked resistors and all sorts of other stuff. Just take your time and bypass the areas with some wire-wrap wire, which is what I use on the cartridges. I've even taken out mapper chips and wired them to other boards and just left the PCB portion hanging loose in the plastic cartridge and it works fine. Don't throw out your "wrecked" cart.

Desoldering
by Lloyd Gordon on 2006-04-24 (#12190)

I just looked at the rest of your post. I use a really cheap radio shack desoldering iron. It costs about $15 and is really crude but works really perfectly on the NES cartridges. I wouldn't use it on anything delicate as it is not EMF isolated and is not temperature controlled.

by tokumaru on 2006-04-24 (#12194)

Lloyd Gordon wrote:
Just take your time and bypass the areas with some wire-wrap wire

What exactly is wire-wrap wire? These kind of terms are a bit hard some times, since I never studied electronics in english... =]

Lloyd Gordon wrote:
Don't throw out your "wrecked" cart.

I guess I'll keep it, as scrap, for now. Maybe some day I'll be able to make something out of it.

Lloyd Gordon wrote:
I use a really cheap radio shack desoldering iron.

I looked so much for one of those and couldn't find any. No stores here have desoldering irons, only (de)soldering stations wich are waaaaaaaaaaay more expensive... I guess I'm stuck with the regular iron and the pump/sucker.

I saw some sockets with longer legs the other day, I guess I'll buy some of those, as they'll allow me to tweak the connections more freely and test what works for a specific chip, before making permanent connections, with regular sockets.

Thanks for the help.

Soldering
by Lloyd Gordon on 2006-04-24 (#12210)

Wire wrap wire is a fairly small guage wire that comes on a spool, single conductor, insulated and the perfect size wire for NES carts. It comes in different colours which is convenient. You can buy a wire wrap tool which makes it really easy to use. It's pretty cheap as is the wrapping tool. Both Amazon and RadioShack have cheap desoldering irons around $10-$13 USD. I don't know if they deliver to Brazil or for how much.

by drk421 on 2006-04-26 (#12255)

Quote:
How do you manege to desolder a socket anyway?

I usually end up breaking them and removing each pin with pliers.

Are you using a desoldering iron? They're only $10 from Radio Shack. well worth the money.

by noriaki_kakyouin on 2006-04-28 (#12351)

So, if I may ask, what is the proper chip modification for the TLROM board? I don't see it on the big list here.

by Bregalad on 2006-04-29 (#12361)

Same as TSROM and TKROM.

by noriaki_kakyouin on 2006-05-01 (#12422)

Would it make a difference if you use 32 or 28 pins for these conversions or is 32 pin EPROMS just assumed to be the accepted?

I ask this myself as i'm starting to find many of my TKROMs that i'm planning on using for my new carts have the 28 pin PRGs in them already and i'm wondering if I should use a 32 pin for all my conversions. I'm just wondering if there's a standard.

by tokumaru on 2006-05-01 (#12423)

The problem is that the largest programmable 28-pin chip you'll find are 64KB in size. I'm not 100% sure, but I don't think there is a programmable 28-pin chip that's 128KB.

I have replaced a 128KB ROM with a 64KB chip in my UNROM devcart. The fact that the pin count was the same made it easier to make the cart, but I made a cart that will not run many commercial games (I only found a couple that used only 64KB). This is likely suited for my own development only.

TKROM boards, however, have holes for the extra pins, even if a 28-pin ROM is originally used. I think the extra holes can be used. Someone will have to clear this up.

by noriaki_kakyouin on 2006-05-01 (#12425)

Thanks, Tokumaru. I hope you can use them.

I will am wanting to burn the translated 'Destiny of an Emperor' onto an EPROM and I see it uses a '512k' PRG chip and a '0k' CHR chip and I was unable to figure out how to proceed using a 'Tecmo Basketball' TKROM board (this is the appropriate board, isn't it?) as that cart's board has a 28 pin PRG chip and a 32 pin-er for the CHR.

And I haven't ordered my EPROMs yet, so I wanted to know what to buy from the place you suggested (FUTURLEC)

by tepples on 2006-05-01 (#12427)

Among TxROM boards used in North American games, only TGROM can support CHR RAM (which iNES calls 0 KB CHR ROM) and 512 KB PRG ROM. You're most likely to find this board in Mega Man 4 or 6. However, TGROM has no PRG RAM. TKROM has CHR ROM, not CHR RAM, and may need a bit of rewiring to get it to work with RAM.

by tokumaru on 2006-05-01 (#12428)

noriaki_kakyouin wrote:
And I haven't ordered my EPROMs yet, so I wanted to know what to buy from the place you suggested (FUTURLEC)

I got the "Flash Memory - Atmel Type" ones. They have all sizes from 32KB (AT29C256) to 512KB (AT29C040).

The 32KB ones work great. I haven't tested the 512KB ones yet, they'll need a lot of rewiring.

Flash ROM's are good if you want to rewrite games over and over. If you plan on keeping the games for good, just buy regular EPROM's (http://www.futurlec.com/ICEPROM.shtml).

by noriaki_kakyouin on 2006-05-01 (#12429)

tokumaru wrote:
Flash ROM's are good if you want to rewrite games over and over. If you plan on keeping the games for good, just buy regular EPROM's (http://www.futurlec.com/ICEPROM.shtml).
I was wanting to make individual carts for each game and keep them for good. Sucks being obsessive/compulsive (laughs).

tepples wrote:
Among TxROM boards used in North American games, only TGROM can support CHR RAM (which iNES calls 0 KB CHR ROM) and 512 KB PRG ROM. You're most likely to find this board in Mega Man 4 or 6. However, TGROM has no PRG RAM. TKROM has CHR ROM, not CHR RAM, and may need a bit of rewiring to get it to work with RAM.
Ah! Thanks for the information.

EDIT: Would this be a good FAQ to follow for the CHR RAM/ROM modification? Is there a better site that shows modification of a TxROM to TGROM? And what RAM chip would I want to order from this page?

Sorry for all the questions. Thanks a lot for helping me learn this.